A switch controller may be used to control the operation mode of a power stage circuit in a buck-boost converter by controlling the switches according to the input voltage and the output voltage. For example, such a control method can include variable frequency control of constant on time or constant off time. However, as phase angles and frequency of the input voltage and the input current may not match each other in variable frequency control, the system may be unstable and a number of components may be needed, which can result in relatively complicated control in some cases.